Alternating-current generator



T. F. WALL ALTERNATING CURRENT GENERATOR.

APPLICATION FILED SEPT-30,1918.

1,356,244, 1 Patented Oct. 19, 1920.

UNITED STATES THOMAS FREDERICK WALL, OF SOUTHSEA, ENGLAND.

ALTEBNATING-CURRENT GENERATOR.

Specification of Letters Patent.

PatentedOct. 19, 1920.

Application filed September 30, 1918. Serial No. 256,317.

T 0 all whom it may concern.

Be it known that I, THOMAS FREDERICK WALL, D. So, D. Eng, subject of the King of Great Britain and Ireland, residing at 48 Nightingale road, Southsea, England, have invented certain new and useful Improvements Relating to Alternating-Current Generators, of which the following is a specification.

I have previously described, the United States Patent No. 1,315,886, a method of producing a sparkless break in an inductive electric circuit involving the use of an asymmetrical pressure wave which reaches the zero value coincidently with the current wave, the circuit being broken at or near the instant of coincidence.

In the application of the principle to the operation of rockdrills, chipping hammers and other reciprocating tools a synchronously operated contact maker is arranged to close the circuit for say a complete cycle and to open the circuit at the end of the cycle, the circuit remaining open for a time corresponding to a number of (for example, three) complete cycles. The plunger which delivers the blow is moved on its working stroke during the cycle for which the circuit is closed and is withdrawn by means of a spring during the time that the circuit remains open.

The object of the present invention is to provide for the operation of rock drills, chipping hammers and other appliances, an alternating current generator which enables a contact maker to be dispensed with.

The invention comprises an alternating current generator adapted to produce asymmetrical pressure waves with relatively long intervals of little or no pressure between the waves. In particular the invention comprises a pair of alternating current generators or an equivalent single machine in which successive complete pressure waves are separated by relatively long intervals of little or no pressure and in which each pressure wave is an asymmetrical resultant of a complete pressure wave and a half pressure wave.

The essential characteristics of the invention will be readily understood from the following description of a particular machine which is applicable to the operation of such reciprocatory tools as rock drills, chipping hammers, riveters and the like.

In the accompanying sheet of explanatory diagrams I Figure 1 illustrates a generator operating in accordance with this invention.

Fig. 2 is a graph of the two pressure Waves produced and Fig. 3 illustrates their resultant together with the current wave.

Fig. 4 shows an alternative auxiliary generator.

Fig. 5 is a graph showing the use of a direct current superimposed on an alternat- 1ng current for producing the required asymmetrical pressure wave.

Imagine a twelve pole single hase generator in which the poles are numbered consecutively 1-12, and in which only the poles 1, 2, 7 and 8 are active, the others bemg removed. The poles thus numbered are indicated by a, Fig. 1. Imagine also a ring armature b carrying two coils situated diametrically opposite to one another the turns of each coil being concentrated together as much as possible. Further suppose the oles 1, 2, 7 and 8 to be respectively N. S. N., then during each revolution of the armature there will be produced two complete but opposite pressure waves with intervals of twice the normal periodicity of the generator between the waves, the normal periodicity being that corresponding to the pole pitch of the poles a.

At first sight it might appear that such a machine would be useful for actuating a reciprocatory rock drill, the current accompanying the pressure waves being utilized to produce the working strokes of the drill and a spring employed to return the drill during the intervals between the pressure waves. Actually, however, the current flowing in such intermediate intervals is sufficient to make the return movements of the drill very slow unless an inconveniently strong spring is used. In order to obtain satisfactory operatwo machines is such that both armature,

windings pass at the same time under 6. g. a N. pole as shown. The two armatures are connected 'in series and in consequence the resultant pressure wave is asymmetrical, the positive half of one wave being greater than the negative half, and the negative half of the next wave greater than the positive half.

Fig. 2 shows the pressure waves obtained from the two generators, 6 being that produced by the main machine and e that produced by the auxiliary machine. Fig. 3 shows at e the resultant pressure wave which is asymmetrical. 11 indicates the current curve.

By suitably adjusting the relative outputs of the two machines the current flowing in the external circuit during the idle intervals can be made sufficiently small and in consequence during such interval the complete idle stroke of the tool can be performed by a spring of moderate strength. It follows from the foregoing that the use of a contact maker for interrupting the external circuit is no longer necessary. Current is taken to and from the external circuit containing the reciprocatory rock drill or the like through slip rings h.

The double machine above described though convenient and practical is given only as an example to elucidate the principle of mypresent invention. Any construction capable of producing asymmetrical pressure waves with intervals during which the pres sure is comparatively small may be employed. For example, the two separate machines may be combined in a single machine, the poles being carried on two separate yokes and the generator windings on the same armature. Also any convenient form of armature may be used.

It will be observed in Fig. 3 that each half of the current wave is entirely positive or entirely nega ive. To neutralize the remanent magnetism of the plunger acted on by the solenoid of the reciprocatory tool prior to each return stroke under the action of the spring it may be advantageous to produce current waves in which a small reversal of current is obtained at the end of each half current wave. This may be effected by adjusting the asymmetry of the pressure wave resenteln this case the current may be caused remain sufiiciently small in the intervals lowed for withdrawal of the plunger by fitting additional poles on the auxiliary genor as shown at 7' in d, the poles (Z nd j l aving alternately N and S polarity.

The best results will probably be obtained by melting the adjustments such that the current curve in the interval allowed for the withdrawal of the plunger crosses the axis again after the abovementioned reversal attaining a small value in the same direction as the immediately preceding principal current wave and then once again crosses the axis after a short interval, gradually in creasing to form the next principal current wave. Tnstead of tie auxiliary alternating current pressure superimposed on the main pressure wave, z. c. on the wave which is characterized by relatively long intervals during which a comparatively small pressure is produced, it is possible to use a direct current pressure obtained from an auxiliary direct current generator or battery, and to superimpose this direct current pressure on the main pressure wave. In this case the main pressure wave should consist of consecutive waves of similar shape and not consecutively reversed waves. F or example, in the case above referred to, poles l. 2. 7. 8. would be respectively N. S. N. S. the other poles being removed. In all cases the rotation should be such that in the resultant pressure the half wave of the larger rea should start the effective current in the external circuit. Fig. 5 shows the efiect ob tained when a direct current pressure is superimposed on an alternating pressure as above desc' ibed. denotes the pressure wave which is symmetrical about the axis as, '5 denotes the current wave and :1 the axis of the resultant pressure wave obtained by superimposing a direct current pressure a on the alternating pressure wave. The axis 1 is also the axis of the current wave z. Relative adjustment of the two pressures may be obtained in any convenient manner. The adjustment may be such that either the current wave never crosses the axis 3 or the current wave may cross the axis and attain such a value in this reverse direction as is found desirable to neutralize the effect of reman'ent magnetism, and thus allow the use of a moder: tely strong spring for withdrawing the plunger.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is 1. Apparatus for producing asymmetrical alternating electrical pressure waves consisting of a generator which produces complete and symmetrical pressure waves with relatively long intervals between the waves and means producing a pressure which when added to the first gives resultant asymmetrical pressure waves, substantially as described.

2. Apparatus for producing asymmetrical alternating electrical pressure Waves consisting of a generator in which successive pairs of poles are separated by relatively long intervals, and means for superimposing on each complete alternating pressure wave a pressure Which is unidirectional during the period of that Wave and produces a resultant asymmetrical Wave, substantially as described.

In testimony whereof I have signed my name to this s ecification.

THO AS F REDERIGK WALL. 

